ENTSO-E Report about Iberian Blackout 

The Expert Panel set up by ENTSO-E to investigate the 28th April 2025 Iberian Blackout published the final report on the 20th of March 2026. The report analyses the root causes of the incident and presents recommendations to strengthen the resilience of Europe’s interconnected electricity system. 

What happened? 

On the 28th of April 2025, the power systems in continental Spain and Portugal suffered a total blackout. A small area in southwest France also experienced a brief disruption. This was the most severe blackout incident on the European power system in over 20 years, and the first one of its kind. 

“At the time of the incident, Spain was exporting electricity to France, Portugal, and Morocco. The event unfolded as a sequence of voltage fluctuations and oscillatory phenomena, which led to widespread generation disconnections in Spain, particularly among inverter-based resources. This was followed by a cascade of overvoltage-related failures, ultimately resulting in the loss of synchronization of the Iberian system with the rest of the Continental European synchronous grid.”, explains Ana Cigarán Romero, Vice-Chair of the ENTSO-E System Operation Committee, the Iberian Blackout. Restoration efforts started immediately. Portugal restored its system within 12 hours and, while Spain required approximately 16 hours.

Findings  

The investigation identifies a combination of interacting factors that led to the blackout in continental Spain and Portugal:

• Oscillations within the system 
• Gaps in voltage and reactive power control 
• Differences in voltage regulation practices 
• Rapid output reductions and generator disconnections in Spain 
• Uneven stabilisation capabilities across the system

The incident was classified as scale 3 incident (Blackout) according to the ICS methodology. It underlines the importance of strengthening system resilience and maintaining strong links between local and European system operations because developments at local level can have system-wide impacts.  

Ana Cigarán Romero emphasizes: „Although we are well positioned, the report shows that national technical measures alone are not sufficient. European grid connection codes must be updated to keep pace with the energy transition and to ensure stable operation of the interconnected system. The 21 recommendations of the expert panel confirm Germany’s System Stability Roadmap. These include the expansion of stabilizing assets, the market-based procurement of reactive power and reserves, as well as the further development of the regulatory framework to make the grid more resilient and future-proof.“ 

Context  
ENTSO-E, which represents 40 electricity transmission system operators (TSOs) from 36 countries across Europe, prepared the report in a technical Expert Panel of 49 members. The panel included representatives from Transmission System Operators (TSOs), Regional Coordination Centers (RCCs), ACER and National Regulatory Authorities (NRAs). Experts from two unaffected TSOs chaired the panel. 

The investigation began on the 12th of May 2025, with data collection and analysis. On October 3, 2025, the panel published a factual report describing the system conditions in April, the detailed sequence of events during the incident, and the restoration process. 

Download the full factual report here: Grid Incident in Spain and Portugal on 28 April 2025 » ICS Investigation Expert Panel » Factual Report » 3 October 2025

In a second phase, the panel assessed the cascading disconnections of generation, voltage control issues and mitigation measures for oscillations. Based on the findings, the panel issued recommendations in its final report, published on the 20th of March 2026, addressing each contributing factor identified and outlining measures to prevent similar events in the future.  

Download the full final report here: Grid Incident in Spain and Portugal on 28 April 2025 » ICS Investigation Expert Panel » Final Report » 20 March 2025